With a recent increase in transmission traffic, the demand for higher speeds and larger capacities of optical transmission systems is increasing. In addition, when Internet of things (IoT) has moved into high gear, it is expected that more devices than those currently used would be coupled at various communication distances.
In optical transmission systems, distortions of waveforms due to wavelength dispersion and the like in transmission lines are compensated for in order to achieve higher speeds and larger capacities, and thus transmission characteristics improve.
In optical transmission systems, the wavelength dispersion value per unit length of signal light varies depending on the type of a transmission line (for example, a single mode fiber, a dispersion shifted fiber, a non-zero dispersion-shifted fiber, or the like). In addition, the wavelength dispersion amount increases in proportion to the length of a transmission line along which signal light propagates. Therefore, the wavelength dispersion amount varies depending on the distance even among transmission lines using the same fiber. Accordingly, in optical transmission systems, the wavelength dispersion amount, which varies depending on the transmission path and the type of a transmission line, has to be estimated for each system and the wavelength dispersion has to be compensated for.
A typical method for controlling a dispersion compensation amount of a tunable dispersion compensator that compensates for wavelength dispersion is, for example, a method in which sweeping is performed for a range set in advance to set the initial value of the dispersion compensation amount (for example, Japanese Laid-open Patent Publication No. 2001-208893).
With an existing tunable dispersion compensator, it takes several seconds to several tens of seconds to adjust the dispersion compensation amount for temperature adjustment or the like. Therefore, when measurement is repeated a plurality of times to set a dispersion compensation amount, it takes a long time until the setting.